Intracardiac surgery for valve replacement has become a common and relatively safe procedure as the instances of specific complications such as technical errors, thromboembolism, and prosthetic failure have diminished. A significant morbidity and mortality remains, however, due to postoperative derangements of the performance characteristics of the LV. It is proposed to evaluate the relative contributions of preoperative and intraoperative factors to the ultimate incidence of LV dysfunction after correction of simulated valvular defects in canine models of valvular heart disease. The effects will be studied of acutely and chronically altered loading states, as seen in valvular heart disease, on left ventricular mechanics using chronically implanted sonomicrometry and solid state micromanometry to directly measure ventricular geometry and pressure in conscious animals. The role which the coronary microcirculation plays in left ventricular dysfunction in these situations will be simultaneously studied by using a) radinucleotide microsphere techniques to estimate the regional distribution of LV blood flow, and b) multiple tracer dilution methods to evaluate capillary transport and the distribution of capillary and shunt flow in the LV myocardium. Acute and chronic abnormalities in LV length-stress characteristics will be correlated to changes in the regional distribution of myocardial blood flow and coronary capillary transport. A final goal is to determine the additional effects of cardiopulmonary bypass on cardiac mechanics and myocardial microcirculation in both normal and hypertrophied ventricles.